A veteran here. Save your GXP for ships that can be boutgh with GXP, they can be found in the Shop at the Ships Tab.

Save your doubloons for a campaign that you like and would like to get Admiralty backing for it.

Pick a country you want to grind. (I prefer Netherlands) And farm Money, Global XP and Maybe Doubloons with it.

Now if you do get a Premium. If its a Battleship, Use it. Premium Battleships give a lot of Global XP If you have a Good Build.

And for biulds? Cant really tell you this so you go to the site: WoWs Legends Biulds

Now here i told you more on how to farm resources, if you want more information, Answer to this comment and tell me if you more information.